The present invention relates generally to optical technology.
Variable optical attenuators are commonly used in optical communication systems and optical measurement systems. A variable optical attenuator (VOA) is a device that is generally designed to adjust the power ratio between a light beam exiting the device and a light beam entering the device over a variable range. Some variable optical attenuators can include Micro-Electro-Mechanical-System (MEMS) devices. A MEMS device generally includes one or more mirrors manufactured on a chip. A mirror on the MEMS device is generally in a tilting angle that can be controlled by a control variable, such as a voltage variable or a current variable.
FIGS. 1a and 1b (prior art) show a VOA 100 that includes a MEMS device 130. VOA 100 also includes a lens 120 and a holder 110 for holding an input fiber 181 and an output fiber 182. Light 101 exiting from input fiber 181 is collimated by lens 120 and is incident upon a reflection surface 131 of MEMS device 130. Light 101 is reflected by reflection surface 131 of MEMS device 130 and becomes light 109. Light 109 is focused by lens 120 to a focus point near the end of output fiber 182. When MEMS device 130 is in a first position, as shown in FIG. 1a, light 109 is focused by lens 120 such that essentially most of light 109 enters output fiber 182. When MEMS device 130 is in a second position with a tilting angle θ, as shown in FIG. 1b, light 109 is focused by lens 120 such that only part of light 109 enters output fiber 182.